Arsenic, Inorganic

Reference Dose for Oral Exposure (RfD) (PDF) (6 pp, 433 K) Last Updated: 01/13/2025

Note: The RfD is based on two organ specific RfDs (osRfDs), which may individually be used in cumulative risk scenarios – (1) 0.058 µg/kg-day (5.8 × 10^-5 mg/kg-day) using a composite UF (UFC) = 3, the osRfD for type 2 diabetes (based on a dose-response meta-analysis of four studies: Grau-Perez et al., 2017; James et al., 2013; Coronado-González et al., 2007; Pan et al., 2013) and (2) 0.057 µg/kg-day (5.7 × 10^-5 mg/kg-day) using a composite UF (UFC) = 3, the osRfD for ischemic heart disease (both fatal and incident cases; based on a dose-response meta-analysis of five studies: Wade et al., 2015; Wu et al., 2010; Moon et al., 2013; Chen et al., 2013; James et al., 2015). See Sections 4.3.7, 4.3.8, and 4.6 of the IRIS Toxicological Review for more information. The RfD of 6.0 × 10^-5 mg/kg-day is the rounded value of these two osRfDs.

Reference Concentration for Inhalation Exposure (RfC) (PDF) (6 pp, 433 K)

Not assessed under the IRIS Program.

Weight of Evidence for Cancer (PDF) (6 pp, 433 K) Last Updated: 01/13/2025

• Bladder and lung cancer are acknowledged as known hazard outcomes for inorganic arsenic (ATSDR, 2007; ATSDR, 2016; Health Canada, 2006; IARC, 2004; IARC, 2012; NRC, 2013; NTP, 2016; WHO, 2011; WHO, 2011), and the strength of evidence for these health outcomes was considered robust (as described in Section 3.2 and Appendix A of the IRIS Toxicological Review). Bladder cancer and lung cancer were classified as carcinogenic to humans in the 1995 IRIS Toxicological Review based on epidemiologic evidence (U.S. EPA, 1995), and that classification is retained in the current assessment.
• This may be a synopsis of the full weight-of-evidence narrative.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure (PDF) (6 pp, 433 K)

Inhalation Unit Risk: 4.3 x 10^-3 per µg/m³
Extrapolation Method: Absolute-risk linear model
Tumor site(s): Respiratory
Tumor type(s): Lung cancer (Brown and Chu, 1983a,b,c; Lee-Feldstein, 1983; Higgins, 1982; Enterline and Marsh, 1982)
Note: The 2025 iAs assessment focused on oral exposures and updated the previous RfD and oral slope factor, but did not update the existing inhalation unit risk (IUR). The IUR listed here (1995) remains in effect (https://iris.epa.gov/document/&deid=364455).